A known slide valve used in this technical field comprises, in general, a stiff frame having walls that define a discharge mouth for discharging the material, and a shutter having the shape of a flat horizontal plate; the shutter, which is moved by an actuator, is translated horizontally and is provided with a surface that is such as to shut/open the aforesaid discharge mouth.
As already mentioned above, a typical application of this kind of valves is the one concerning the opening/shutting of the bottom of silos or of any kind of hopper.
One of the technical problems affecting these slide vales is that of preventing the material from leaking from the shutter when the latter is in a discharge mouth shutting position and, furthermore, of preventing the powdered material, which sticks to the upper surface of the horizontal shutter, from being dragged and forced to leak through the passage slit of the horizontal shutter during the opening of the discharge mouth, namely when the shutter is retracted by the actuator.
A further problem that can arise when using this kind of valves for hoppers is that the lip of the gasket pressed against the upper surface of the shutter scrapes against this surface during the movements of the shutter and, therefore, the lip, in time, is subject to wear and looses or, anyway, decreases its capability to forbid the leaking of powdered material from the discharge hopper towards the hydraulic or pneumatic actuator, which is responsible for the forward and backward movements of the shutter itself.
All this can lead to the negative consequence that the shutter of the valve might not be able to perform the entire travel and completely open the discharge mouth, thus jeopardizing the speed with which the hopper standing above the valve is emptied. In the worst case scenario, the downward flow of the material could be stopped.